Beyond the Thymus

Tonsils Make T-Cells Too

T lymphocytes (T cells) have been thought to develop only in the thymus, but a study led by OSUCCC – James researchers suggests they can also develop in human tonsils. This finding could improve the understanding of T-cell cancers and autoimmune diseases, as well as how stem-cell transplantation is done.

The study identified T cells at five stages of development in the tonsils. These stages, revealed by molecular signposts on the cells, were very similar to the stages of T-cell development in the thymus, although some differences were found. The study also discovered that the cells develop in areas near the fibrous scaffold of the tonsil.

“We’ve known for a long time that a functional thymus is necessary to develop a complete repertoire of T cells, but whether a T-cell factory existed outside the thymus was controversial,” says principal investigator Michael A. Caligiuri, MD, director of the OSUCCC and CEO of The James. “I believe our study answers that question. It is the first to describe a comprehensive, stepwise model for T-cell development outside the thymus.”

It also raises other questions. Caligiuri says it is still unclear whether T cells that develop in the tonsils also mature there or leave to mature elsewhere.

“The complete implications of this phenomenon for human health and disease are not entirely known,” adds first author Susan McClory, a graduate fellow in Caligiuri’s laboratory. “It could be important in the development of T-cell cancers and autoimmune diseases, or it might suggest a location for T-cell development when thymus function is poor. We hope to explore these possibilities.”

“Our work suggests that the
tonsils serve as a T-cell factory, along with the thymus,” Caligiuri says. “Next we need to learn what proportion of T cells is derived from the tonsils compared with the thymus.”